Electrical contact device



3,226,517 ELECTRICAL CONTACT DEVICE Horst Schreiuer, Numberg, Germany, assignor to Siemens-Schuckertwerke Aktiengesellschaft, Berlin- Siemensstadt, a corporation of Germany Filed Sept. 24, 1962, Ser. No. 225,928 Claims priority, application Germany, Sept. 26, 1961, S 75,926 6 Claims. (Cl. 200166) My invention relates to sintered contacts for electrical switches, relays and other contact apparatus.

It is an object of my invention to provide a sintered stratified contact structure which affords a considerable simplification and reduction in cost with respect to the manufacture of the contacts and also results in improved contact structures free from the danger of layer separation under high load conditions.

According to my invention, the electric contact body comprises a sintered contact layer of good electric contacting properties but relatively poor weldability as well as of a likewise sintered backing layer of good weldable metal, the two layers being both produced simultaneously by the powder-metallurgical method in substantially the ultimate shape of the body and are thus intimately sinter-bonded together.

In order that the present invention may be readily carried into effect, it will now be described with reference to the accompanying drawing, wherein:

FIG. 1 is a flow diagram of a production method of the prior art;

FIG. 1a is a cross-section of an embodiment of a contact device produced by the method of FIG. 1;

FIG. 2 is a flow diagram of an embodiment of the production method of the present invention;

FIG. 2a is a cross section of an embodiment of a contact device of the present invention; and

FIG. 2b is a cross section of another embodiment of a contact device of the present invention.

Known contact bodies for the above-mentioned purposes consist of two layers, namely a good contacting contact material proper and a backing layer of good weldable metal. For example, the contact layer as shown at 1 in FIG. 1a may consist of silver, copper or alloys thereof, whereas the backing layer (2 in FIG. 1a) may consist of iron, nickel, Monel (Ni-Cu alloy in the ratio 75:25) or a similar good weldable metal. It has become known to produce the contact layer 1 by the powder-metallurgical methol, namely, according to FIG. 1, from pulverulent material by pressing and thereafter sintering, followed by rolling the sintered body. The further porduction has been carried out by plating the contact material and the good weldable metal upon each other, for example by another hot-rolling or cladding process. Thereafter the contact bodies are produced from the resulting two-layer sheet material by punching, embossing or cut ting. This process is relatively expensive and the two layers may occasionally become separated from each other when the finished contacts are subjected to high electric and thermal loads. I

According to a feature of my invention, relating to the contact design in which the contact layer proper and the welding layer consist of respective materials that cannot be satisfactorily bonded together by the sintering method, an intermediate layer as shown at 5 in FIG. 2b is lo cated between the contact layer 1 and the weldable backing layer 2 and is jointly bonded and shaped with the other layers by a powder-metallurgical sinter method so that the three layers form together a single integral structure. The intermediate layer, to serve the just-mentioned purpose, must consist of a material that can be bonded with United States Patent 0 the respective materials of the two other layers by sintering.

The term poorly weldable contact materials is herein understood to relate to materials whose weldability is appreciably below that of iron which is being considered here, together with nickel and Monel, as a measure of a good weldable metal.

The production method according to the invention is diagrammatically represented in FIG. 2. The material for the contact layer (1 in FIGS. 2a and 2b) and the powder for the backing or welding layer 2 and, as the case may be, the powder for the intermediate sintering layer (5 in FIG. 2b) are separately prepared and are then successively filled into a mold or die to form two or three layers. These two or three layers are then jointly compressed to form a shaped body in accordance with the shape of the ultimate product to be obtained. Thereafter the press-molded body is subjected to sintering and then furnishes the finished contact structure. In some cases it is desirable, however, to subject the sintered product to subsequent pressing operation at a higher pressure than employed prior to sintering, for the purpose of giving the product its ultimate shape or density.

A comparision of the two flow diagrams shown in FIGS. 1 and 2 will illustrate the considerable simplification obtained by virtue of the invention. In addition, the layers that constitute the shaped contact structure are much more intimately bonded together so that a subsequent separation between the sintered strata is virtually excluded regardless of the amount of electrical load or temperature to which the contact may be subjected during its electrical operation.

A contact body designed and made according to the invention is preferably joined with its carrier, such as the structure 4 shown in FIG. 2a, by welding. It is another advantage of the invention over the prior art that the shape of the welding layer 2 can readily be adapted to the particular welding method to be employed for welding the contact body to its carrier without requiring any additional expedient or manufacturing step. For example, such contacts are often connected with the carrier 4 by spot or boss welding which makes it necessary or desirable to provide the weldable backing layer 2 with a rearward boss 3 or protrusion, or several such bosses. According to the known contacts, this necessitated the above-mentioned embossing or operation or machining by cutting tools. The contact according to the invention, however, can readily be provided with any desired bosses 3 simply by press-molding the pulverulent body accordingly. Welding bosses as shown at 3 are desirable, for example, in cases where the welding layer 2 consists of iron, nickel and Monel. In cases where the metal of the carrier structure 4 has a lower melting point than the backing layer 2, for example, when the carrier structure 4 consists of bronze or brass, the contact body can also be butt-welded upon the carrier 4 and the rear surface of the backing layer can then be given a planar shape. In any event, the shape of the welding layer 2, depending upon the particular welding method to be used, can simply be obtained by giving the pressing plunger the corresponding shape, thus requiring no additional fabricating step.

In cases where it is essential that the contact material in layer 1 have a highest feasible density, the contact body according to the invention can be densified virtually up to its theoretical density by employing the above-mentioned pressing step subsequent to the sintering operation. This subsequent pressing and the resulting flow of material of the contact layer and the welding layer results in a finished body of particularly accurate shape and dimensions.

The invention is further illustrated by the following embodiments and production methods:

3 Examp e 1 Employed for the contact layer 1 was an Ag-Ni powder mixture in the ratio 90/ 10. Nickel powder was used for the welding layer. Filled into a matrix having a pressing area of 10 mm. diameter were 0.35 g. carbonyl nickel powder with a grain size below 10 micron, and thereafter 1.5 g. of the Ag-Ni powder mixture. The powder was then compressed at a pressure of 1 ton/cm The resultinng shaped body was subsequently sintered at 850 C. for one hour in a hydrogen atmosphere. The sintered body was subsequently pressed at 8 ton/cm}. During sintering, the nickel layer shrinks somewhat more than the Ag Ni layer. The subsequent pressing results in a contact body of finished shape. Machined into the lower plunger of the press is the shape of a boss 3 having a diameter of 4 mm. and the height of 0.5 mm., resulting in a product corresponding to that shown in FIG. 2a. The contact structure can readily be boss-welded upon a contact carrier 4 of iron.

Example 2 Used for the contact layer was Ag-C powder in the ratio 96/4. Used for the intermediate layer 5 was pure silver, and for the welding layer 2 iron. Filled into the press matrix mentioned under Example 1 were 0.4 g. carbonyl iron powder having a grain size below 5 micron, thereafter a layer of 0.2 g. electrolysis silver powder with a grain size below 60 micron, and thereafter 0.8 g. of a powder mixture composed of 96% electrolysis silver powder and 4% graphite powder having a grain size below micron (the percentages being by weight). The three layers were then compressed in a plunger press at a pressure of 1.5 t./cm. The resulting shaped bodies were sintered at 880 C. for one hour in vacuum (below 10- mm. Hg). The sintered body was subsequently subjected to compression at a pressure of 8 t./cm. resulting in a contact structure of finished shape, and attaining virtually the theoretical density in the contact layer 1 and in the welding layer 2. The contact body can readily be bosswelded on a carrier of iron. The press-molded body can be welded upon the carrier right after the sintering step, and the densification by subsequent pressing can be performed together with the carrier structure. When, in the above-described example, the subsequent densification is performed at 3 t./cm. the contact layer and the intermediate layer will possess a residual porosity corresponding to a space-filling degree of 0.9 to 0.99.

In the methods otherwise corresponding substantially to the above-described examples, other contact metals can also be used. Thus, the contact metals Ag-Pb, Cu-Pb, Ag-CdO, Ag-SnO Ag-Ni-Cd can be provided with a corresponding welding layer. When the contact metals contain tungsten, as is the case with such compositions as W-Cu, W-Ag, W-Cu-Ni, W-Ag-Ni and W-Cu-Ag-Ni, the good welding layer 2 may consist of Ni-Cu alloy in the raio 75/25 (Monel). In these cases it is advisable to employ a molding pressure of 3 t./crn. and a sintering temperature of 1250 C. for one hour in hydrogen.

When Ag-C is employed as contact layer 1 together with a welding layer consisting of Ag-Cu with a content of copper, for example 8% Cu, then the contact body need not be provided with bosses at the good weldable backing layer 2 but can be given a planar rear surface and be butt-welded upon a carrier structure 4 of brass or bronze. The Ag-Cu welding layer may also be given a higher copper content and is then particularly well suitable for butt welding at a lower electrical conductivity than To those skilled in the art it will be understood, upon studying this disclosure, that with respect to details in design and shape as well as relative to individual materials and correspondingly adapted temperatures and pressures, my invention permits of various modifications and can be given embodiments other than particularly illustrated and described herein, without departing from the essential features of the invention and Within the scope of the claims annexed hereto.

I claim? 1. An electrical contact device, comprising a contact layer of material having a weldability less than that of iron; and

a welding layer of material having a weldability at least as good as that of iron, said contact layer and said welding layer forming an integral powder-metallurgical unit of integrally shaped and solidified structure, said welding layer material comprising one of a group consisting of nickel-copper, nick-e1 powder, iron carbonyl, iron powder and silver copper.

2. An electrical contact device as claimed in claim 1, further comprising an intermediate layer of material positioned between and integrally formed with said contact layer and said welding layer.

3. An electrical contact device as claimed in claim 1, further comprising an intermediate layer of pure silver positioned between and integrally formed with said contact layer and said welding layer.

4. An electrical contact device, comprising a contact layer of material having a weldability less than that of iron, said contact layer material comprising a powder mixture of silver and nickel in a ratio of to 10; and

a welding layer of material having a weldability at least as good as that of iron, said contact layer and said welding layer forming an integral powder-metallurgical unit of integrally shaped and solidified structure.

5. An electrical contact device, comprising a contact layer of material having a weldability less than that of iron, said contact layer material comprising a powder mixture of silver and graphite in a ratio of 96 to 4; and

a welding layer of material having a weldability at least as good as that of iron, said contact layer and said welding layer forming an integral powder-metallurgical unit of integrally shaped and solidified structure.

6. An electrical contact device, comprising a contact layer of material having a weldability less than that of iron, said contact layer material comprising one of a group consisting of silver-nickel, silver-graphite, silver-lead, silver-cadmium oxide, silver-stannic oxide, silver-nickel oxide, copper-lead, tungsten-copper, tungsten-silver, tungsten-coppernickel, tungsten-silver-nickel and tungsten-copper-silyer-nickel; and

a welding layer of material having a weldability at least as good as that of iron, said contact layer and said welding layer forming an integral powder-metallurgical unit of integrally shaped and solidified structure, said welding layer material comprising one of a group consisting of nickel-copper, nickel powder, iron carbonyl, iron powder and silver copper.

References Cited by the Examiner UNITED STATES PATENTS 2,414,463 l/1947 Gunn et al 200--166 2,464,591 3/1949 Larsen et a1 29-l55.55 2,706,759 4/1955 Williamson 200-l66 2,925,647 2/1960 Ioneset al. 29l55.55 3,034,202 5/1962 Graves 29--l55.55 3,106,628 10/1963 Chiswcll 200-166 FOREIGN PATENTS 749,390 5/1956 Great Britain.

KATHLEEN H. CLAFFY, Primary Examiner.

BERNARD A. GILHEANY, Examiner. 

1. AN ELECTRICAL CONTACT DEVICE, COMPRISING A CONTACT LAYER OF MATERIAL HAVING A WEIDABILITY LESS THAN THAT OF IRON; AND A WELDING LAYER OF MATERIAL HAVING A WELDABILITY AT LEAST AS GOOD AS THAT OF IRON, SAID CONTACT LAYER AND SAID WELDING LAYER FORMING AN INTEGRAL POWDER-METALLURGICAL UNIT OF INTEGRALLY SHAPED AND SOLIDIFIED STRUCTURE, SAID WELDING LAYER MATERIAL COMPRISING ONE OF A GROUP CONSISTING OF NICKEL-COPPER, NICKEL POWDER, IRON CARBONYL, IRON POWDER AND SILVER COPPER. 